Influence of silica content in sulfonated poly(arylene ether ether ketone ketone) (SPAEEKK) hybrid membranes on properties for fuel cell application

Sulfonated poly(arylene ether ether ketone ketone) (SPAEEKK) copolymer containing pendant sulfonic acid group (sulfonic acid content (SC) = 0.67) was synthesized from commercially available monomers such as sodium 6,7-dihydroxy-2-naphthalenesulfonate (DHNS), 1,3-bis(4-fluorobenzoyl)-benzene (BFBB), and hexafluorobisphenol A (6F-BPA). SPAEEKK/silica hybrid membranes were prepared using the sol-gel process under acidic conditions. The SPAEEKK/silica hybrid membranes were fabricated with different silica contents and the membranes were modified to achieve improved proton conductivity incorporating P-OH groups (H₃PO₄ treatment).The silica particles within the membranes were used for the purpose of blocking excessive methanol cross-over and for forming a pathway for proton transport due to water absorption onto the hydrophilic SiOH surface. The proton conductivities of H₃PO₄-doped membranes were somewhat higher than the un-doped (H₃PO₄-free) membranes due to increasing hydrophilicity of the membranes. The presence of silica particles within the organic polymer matrix, which decreases the ratio of free water to bound water due to the SiOH on the surface of silica derived from sol-gel reaction, results in hybrid membranes with reduced methanol permeability and improved proton conductivity.